1. Understand the Formula

Ammonium sulfide has the formula (NH₄)₂S. This means each molecule contains:

* 2 nitrogen atoms (N)

* 8 hydrogen atoms (H)

* 1 sulfur atom (S)

2. Use Avogadro's Number

Avogadro's number tells us that there are 6.022 x 10²³ particles (atoms, molecules, etc.) in one mole of a substance.

3. Calculate the Number of Hydrogen Atoms

* Moles of hydrogen atoms: Since each ammonium sulfide molecule has 8 hydrogen atoms, 3.90 mol of ammonium sulfide contains 3.90 mol * 8 = 31.2 mol of hydrogen atoms.

* Number of hydrogen atoms: Multiply the moles of hydrogen atoms by Avogadro's number: 31.2 mol * 6.022 x 10²³ atoms/mol ≈ 1.88 x 10²⁵ hydrogen atoms

Therefore, there are approximately 1.88 x 10²⁵ hydrogen atoms in 3.90 mol of ammonium sulfide.